Property-Set and Query Events
There are four predefined events related to properties:
- PreSet — Triggered just before the property value is set, before calling its set access
method - PostSet — Triggered just after the property value is set
- PreGet — Triggered just before a property value query is serviced, before calling its
get access method - PostGet — Triggered just after returning the property value to the query
These events are predefined and do not need to be listed in the class events block.
When a property event occurs, the callback is passed an event.PropertyEvent object.
This object has three properties:
- EventName — The name of the event described by this data object
- Source — The source object whose class defines the event described by the data
object - AffectedObject — The object whose property is the source for this event (that is,
AffectedObject contains the object whose property was either accessed or
modified).
You can define your own property-change event data by subclassing the
event.EventData class. The event.PropertyEvent class is a sealed subclass of
event.EventData.
See “Listen for Changes to Property Values” on page 11-40 for a description of the
process for creating property listeners.
See “The PostSet Event Listener” on page 11-60 for an example.
See “Property Access Methods” on page 8-50 for information on methods that control
access to property values.
Listeners
Listeners encapsulate the response to an event. Listener objects belong to the
event.listener class, which is a handle class that defines the following properties:
Event and Listener Concepts